A basic precept of wireless communication is that a radio cannot transmit and receive on the same frequency at the same time, i.e. operate in a co-frequency/time full duplex fashion. The signal from a local transmitting antenna is much stronger than transmissions from other nodes, which has been attenuated by the propagation loss. Hence it has been generally assumed that one cannot decode a received signal at a radio while it is simultaneously transmitting.
To achieve send and receive data in a co-frequency and co-time way, under the current cellular system assumption, the required interference cancellation capability has to be 130˜140 dB. Externally and internally, now 80 dB interference cancellation can be achieved.
To enhance the interference cancellation capability, some aspects can be considered, where different implementation complexity can be observed for base station and user equipment's.                To increase the loss provided at antenna, geographically separated transmitter and receiver antennas can reduce the interference received at the receiver port largely. It is easier to implement at base station (BS) side, considering the smaller size of the user equipment, UE.        To deal with the interference, the cancellation algorithm has to track Doppler and multi-path effect perfectly. Due to this, a fixed side BS would experience a more stable environment, and would be less affected by mobility, e.g. at UE side.        
So to benefit from full duplex scheme, while not imposing too much complexity at UE side, the full duplex interference cancellation can be applied only at BS side, while two different UEs are scheduled for the downlink (DL) and uplink (UL) direction. And the problem is converted to how to avoid the UE to UE interference in this case.
Considering a co-frequency/time full duplex scheduling in a single cell, the harmful interference is in two aspects:
1) the self-interference from BS transmit antenna to BS receive antenna; and
2) the UE to UE interference from UL UE to DL UE.
In the international patent application WO 2013/004283 it is presented a straightforward UE-to-UE measurement to get UE-UE link loss information. However, legacy UEs are not configured to perform direct UE to UE measurement